Generally, a hydraulic excavator as a representative example of a construction machine is constituted by an automotive lower traveling structure, an upper revolving structure swingably mounted on the lower traveling structure, and a working mechanism liftably mounted on the front side of the upper revolving structure.
The upper revolving structure is provided with a revolving frame serving as a support structural member, an engine mounted at the rear side of the revolving frame, and a cab located at the left front side of the revolving frame to be positioned along the left side of the working mechanism, wherein an operator's seat in which an operator is seated and the like are provided in the cab.
A fuel tank is provided in the revolving frame to be positioned in the right side of the working mechanism for reserving fuel supplied to the engine, and an article accommodating box is provided in front of the fuel tank for accommodating articles such as tools, a grease gun, and various consumables.
On the other hand, a diesel engine is adopted as the engine in the hydraulic excavator, and the diesel engine is supposed to discharge a large amount of nitrogen oxides (hereinafter referred to as NOx) and the like. Therefore, a NOx purifying device for purifying NOx is as a post-treatment device of the exhaust gas in the diesel engine. The NOx purifying device, for example, is constructed to accommodate a urea selective reduction catalyst for removing NOx in the exhaust gas in an accommodating tubular casing provided in the halfway of an exhaust pipe of the engine. Therefore, the hydraulic excavator is provided with a urea water tank for reserving a urea solution as a reducing agent and a urea water injection valve for injecting the urea solution in the urea water tank toward the upstream side of the urea selective reduction catalyst, and the urea water tank is connected to the urea water injection valve by a connecting pipe.
In a case of providing the urea water tank in a hydraulic excavator, it is desired to set a tank capacity to be large for reducing the number of supply times of the urea solution. However, since many devices are mounted on the hydraulic excavator, it is difficult to furthermore secure a space for locating the urea water tank. Therefore, there are some cases where the conventional hydraulic excavator is constructed to accommodate the urea water tank in an article accommodating box for accommodating tools and the like (for example, Japanese Patent Laid-Open No. 2008-240676 A).